“…The molecules concerned are metabolites of the purine degradation pathway, such as AMP, adenine, guanine, hypoxanthine, xanthine, and uric acid, secreted in response to the starvation conditions or physiological stress induced during sample preparation and signal acquisition. [66][67][68] However, even if these small molecules, slightly soluble to soluble in water, are found in the bacterial supernatant, it must be noted that their concentration is largest in the extracellular regions near the outer cell walls. Indeed, here are located enzymes (e.g., phosphoribosyltransferase) that convert purine mononucleotides to purine bases and derivatives and transport the products across cell membranes.…”